<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        div {
            width: 200px;
            height: 50px;
            background: yellow;
            border: 1px solid red;
            margin: 0 auto;
            text-align: center;
         
        }

        ul {
            /* display: none; */
            margin-top: 50px;
            height: 0px;
            overflow: hidden;
            transition: all 2s;
            
        }

        div:hover ul{
            /* display: block; */
            height: 200px;

        }

    </style>

</head>

<body>
    <div>
        我的菜单
        <ul>
            <li>1111</li>
            <li>2222</li>
            <li>3333</li>
            <li>4444</li>
            <li>5555</li>

        </ul>

    </div>
</body>

</html>